This invention relates to coaxial connectors for connection to coaxial cable plugs and more particularly to a coaxial cable and connector assembly for connection to a Super High Frequency (SHF) low impedance (Zl) electrical circuit element for conducting SHF signals between the element and a coaxial port of the connector that accepts and matches a conventional relatively high impedance (Zh) coaxial cable.
Heretofore, a coaxial cable and connector assembly for direct connection of the cable part thereof to a low impedance (ten ohm), high frequency circuit element operating in the SHF range of 0.5 to 20 GHz and higher has been provided to users in the form of a coaxial cable four to six inches long with a conventional fifty ohm coaxial connector at one end. The cable is of special construction and incorporates a series of transformer steps from the ten ohm end that connects to the SHF circuit element to the fifty ohm end attached to the conventional fifty ohm connector that provides a port for a fifty ohm coaxial cable plug. The object here is to use a conventional fifty ohm SHF connector for the port and so the cable to the SHF circuit element is of special construction and contains a ten to fifty ohm coaxial transformer to insure acceptable voltage standing wave ratio (VSWR) at SHF operation.
It has been the practice to make the special cable of a length of Number 070, 10 ohm coaxial cable by disassembling the cable, machining the center conductor to form transformer steps, boring the dielectric to fit the machined center conductor and then, reassembling the cable for attachment to the connector. Clearly, this cable and connector assembly cannot be made with a connector at each end of the special cable to provide the user with two cable and connector assemblies by cutting the cable at a suitable point between the two connectors as described in my co-pending U.S. patent application Ser. No. 686,932, filed Dec. 27 1984 and entitled "Method And Means of Construction of Coaxial Cable And Connector Assembly". The product described in that application provides the user with two 50 ohm to 50 ohm SHF cable and connector assemblies for providing two coaxial ports to the circuit.
At SHF frequencies of 0.5 to 20 GHz, or higher, the cable of the assembly is as small as Number 070 50 ohm cable (0.070 inches in diameter) and the threads of the connector attached to the cable are 7/16 inch by 28 threads per inch and so the connector is also quite small. My co-pending application teaches a technique of connecting an even smaller cable and connector so that the two fit together in intimate electrical and mechanical contact that withstands separation forces specified, without soldering the cable and connector together.
The technique described in my said co-pending application is used to provide a 50 ohm impedance electrical connection to SHF circuit elements such as a YIG filter
These assemblies are sometimes called "YIG cable assemblies". They provide a connection to the YIG filter for a conventional fifty ohm coaxial cable plug external of the YIG circuit. As described in that application, the cable assembly is provided with a length of fifty ohm cable (Number 047, 50 ohm), four to six inches long and a fifty ohm connector attached to each end. The user cuts the cable to the length desired and uses each half to make a connection for a conventional fifty ohm coaxial cable port. Each is used by baring the fine, wire-like center conductor of the cable a sufficient length for attachment to the YIG filter.
Prior to my invention described in my co-pending application, such a cable assembly was made by inserting a bared end of the Number 047, 50 ohm cable with the wire-like center conductor thereof projecting, into an accommodating end of a fifty ohm connector so that the center conductor of the cable would fit inside a spring finger at that end of the connector center conductor. Then, the outer conductor of the cable was soldered to the connector housing. Following that, epoxy was applied around the connector center conductor, dielectric and housing through a hole provided therein to fix them in position and so insure that radial and axial alignments of the connector center conductor, dielectric and housing are maintained during use. This technique was sometimes referred to as "epoxy captured contacts".
At the assembly of the cable and connector, the bared end of the cable that was inserted into an accommodating part of the connector, was inserted before the capturing epoxy was applied around the connector parts to fix their positions, and then the cable was soldered to the connector. The capturing epoxy could not be applied before inserting the cable and soldering, because the heat of soldering would so effect the epoxy that it would not be effective to fix the parts in position. At that assembly, when the bared cable was inserted into the connector accommodation, any misalignment of the connector spring finger and cable center conductor would at least force either or both out of position with respect to the outer conductors and so would likely impair electrical performance, or, at worse, bend the very thin cable center conductor so that it either would not contact the connector center conductor spring finger or it would short to the connector housing. As a consequence, fabrication of such cable-connector assemblies suffered a high rejection rate.
As described in my co-pending application, the cable has a conductive ferrule attached to an end to the outer conductor thereof and the outside diameter of the ferrule provides a smooth electrically conductive cylindrical surface. The coaxial connector of the same impedance as the cable has a coaxial recess at one end to accommodate a force fit therein with the outer diameter of the ferrule. At assembly, the ferrule is force-fit into the connector recess while the cable wire-like center conductor that projects from the end of the cable and is enclosed by the ferrule engages an accommodating connector center conductor spring finger and slides inside the finger, making mechanical and electrical connection therewith. The fit between the ferrule and the connector recess is sealed with an epoxy applied to the outside of the connector, sealing the points of connection of the cable and connector conductors inside the connector.
According to my co-pending application, assembling the cable and connector is facilitated using a transverse hole through the housing and dielectric to the center conductor so that epoxy can be inserted therein while the housing and center conductor are held in fixed concentric alignment, so that when the epoxy hardens the aligment is maintained. Thus, the connector contacts are "epoxy captured". Following that step, the ferrule, soldered to the end of the cable, is inserted into the coaxial recess and the center conductor of the cable within the ferrule precisely meets the connector center conductor spring finger. This alignment must be near perfect and must be maintained as the ferrule is force-fit into the recess in the connector housing. An annular recess set back from the inserted end of the ferrule and a counter recess at the entrance to the connector housing recess are provided so that when the ferrule is force fit into the connector housing recess, an annular space is defined at the recess entrance to accept epoxy that seals the fit of the ferrule to the connector and so the electrical connections between the two are sealed within the connector by this epoxy.